1. Field of Invention
The apparatus and techniques described herein relate to non-intrusive monitoring by sensing physical parameters such as electric and/or magnetic fields. Such apparatus and techniques may find application in a variety of fields, such as monitoring consumption of electricity, water, etc., in homes or businesses, for example, or industrial process monitoring.
2. Discussion of the Related Art
Among the many potential benefits identified by the U.S. Department of Energy, the smart grid promises enormous energy savings through cost-effective demand-side energy management. Reducing the power consumed by utility customers by just 5% would equate to permanently eliminating the fuel and greenhouse gas emissions from 53 million cars. The accessibility of power monitoring information will be a critical driver for the success of these efforts. Centralized power monitoring systems promise lower sensor count than other per-load sensor systems. Several references describe centralized power monitoring approaches in which loads are identified and then monitored according to their current signatures. Closed or clamp core sensors wrapped around the utility feed are often used to provide current sense signals. These sensors are impractical in many retrofit applications. For instance, skilled labor is required to separate line and neutral in order to deploy a wrap-around sensor, and in some industrial environments electrical service interruption may be unacceptable or prohibitively expensive.
There are several patents describing non-contact power monitoring. EP0176634A1 describes a Hall Effect sensor for monitoring multiple conductor cables, but only for a two-wire conductor and for a specific wire rotation. Numerous patents describe a circuit breaker with integrated current monitoring (for example, U.S. Pat. No. 5,196,982), but all of the described techniques require replacement of the existing breaker. U.S. Pat. No. 6,330,516 describes magnetic sensors arrayed around a breaker panel but does not describe a signal processing technique that can be used to recover to current and voltage information from these sensors or what type of sensors are actually used. It is unclear how the described system could be implemented in practice.
In addition to electrical services, premises such as homes or businesses may receive utility services such water and natural gas services. A premises may be equipped with a water meter that measures the total amount of water consumed and/or a gas meter that measures the total amount of natural gas consumed. A conventional water meter has a display that a user may view to see the total amount of water that has passed through the water meter. More recently, a new type of water meter has been developed that has built-in a wireless communication capability for wirelessly sending the information representing the total amount of water that has passed through the water meter to an external computing device. However, installing such a water meter may require the services of a trained professional, and thus may be prohibitively expensive.